This application is related to copending application Ser. No. 558,226 filed Mar. 14, 1975.
The invention relates generally to an elevator for an earth-moving scraper and more particularly to a high inertia drive having torque capability to overcome normal peaks of loading but with provision for protecting the mechanism, internally against build-up of torque to a destructive level and externally against applied blows or other abuse.
An elevator used with a large scraper bowl must operate constantly under abusive conditions since, in addition to elevation of soil, the elevator must successfully accommodate all sorts of surface debris including boulders of various size, branches and roots, and often timbers and other heavy trash resulting from previous land fill. In order to prevent stalling in the face of normal peaks of loading while keeping the drive motor down to reasonable size, it has been known to employ a flywheel on the motor shaft. Unfortunately, when an elevator flight suddenly encounters a large boulder or similar obstruction, resulting in blockage of the flight, chains and drive shaft, the flywheel tends to continue to rotate because of its momentum. The sudden deceleration results in the setting up of a destructive torque which may result in over-stress or even breakage of one of the shafts or gears in the gear box. In short, the energy stored in the rotating system becomes of destructive effect.
Attempts have been made to provide some relief from peak torques by using an interposed fluid coupling. However, this has not worked out satisfactorily since the torque transmitted by a fluid coupling varies in accordance with the speed differential between the input and output elements resulting in relatively poor protection against suddenly imposed overloads while suffering slippage and loss of driving efficiency under more normal conditions. Also shear pins have been employed in order to preserve driving efficiency, but this results in expensive down time when replacement is required, and even disablement of the machine when the operator, as is likely, runs out of pins for replacement purposes.
With regard to external protection, it is the practice to mount the gear box and motor, stacked upon one another, in an outwardly projecting position at the top of the elevator where the assembly is exposed to self-inflicted blows when maneuvering in close quarters or to blows from other mobile equipment.